While the invention is applicable to the purification and treatment of water in general, it is particularly applicable to the treatment of water in pools, spas, and in confined ponds where the same body of water is retained, often for periods of many years, without replacement except for the addition of water to compensate for evaporative loss. Thus, the invention is applicable to the maintenance of purity and sanitary conditions within decorative pools and lagoons and recirculating fountains, and in swimming pools and spas.
Water treatment in that application ordinarily consists of a combination of chemical treatment and mechanical filtering. Filtering is accomplished by drawing a stream of water from the pool, usually with a centrifugal pump, forcing it through a mechanical filtering bed and returning the water to the pool. That kind of circulation system is provided primarily to accomplish filtering, but availability of the system makes it convenient to include a facility for heating the water in that same circuit. The existence of a circulation system makes it easy to accomplish chemical treatment. It is necessary only to add a quantity of treatment material in liquid or soluble form, and the circulation system will soon ensure adequate dispersal of the treatment material.
In most cases, the primary purpose for water treatment is to destroy the living bacteria and algae material. That can be done by adding oxidizing agents such as chlorine, iodine and oxygen, and by the addition of certain metallic ions. The addition of copper ions is well known as an aid in destroying algae. The addition of silver ions is well known as an aid to killing bacteria. The most widely used agent for destroying bacteria and algae is chlorine. Chlorine is gaseous at ordinary temperatures and it is not generally available, and is difficult to handle as a gas. As a consequence, the chlorine that is used in pool and pond water treatment is included as a constituent of some compound which is made to dissociate after addition to the pool or pond water. Chlorine is often introduced as a constituent of calcium hypochlorite, a popular form of which is sodium dichloro-S-triazinetrione, sodium hypochlorite and chlorinated isocyanurates, or some other acid, or as a salt. If it is introduced as part of a salt, it is usually required to add additional materials to avoid accumulations of the other constituent in the salt. The result is that the treatment of the water in most pools and ponds becomes a problem of chemical balance requiring the addition of chemicals to counteract the effect of the addition of other chemicals. The amount of chlorine or other agent that is required varies from time to time with the amount of usage in the case of swimming pools and spas, and with seasons and holiday activities in the case of decorative pools and fountains which are frequented by birds and windborne living matter, or which become the recepticle for the used food containers and cigaret remains and the like.